Methods for Forming a Semiconductor Device and Semiconductor Devices

ABSTRACT

A method for forming a semiconductor device includes forming a plurality of non-semiconductor material portions at a first side of a semiconductor substrate; forming semiconductor material on the plurality of non-semiconductor material portions to bury the plurality of non-semiconductor material portions within semiconductor material; removing at least a portion of the semiconductor substrate from a second side of the semiconductor substrate to uncover the plurality of non-semiconductor material portions at a backside of the semiconductor device; and forming a rough surface at the backside of the semiconductor device by removing at least a subset of the plurality of non-semiconductor material portions while at least a part of a semiconductor material located laterally between the plurality of non-semiconductor material portions remains or by removing at least a part of a semiconductor material located laterally between the plurality of non-semiconductor material portions while the plurality of non-semiconductor material portions remain.

This application claims priority to German patent application No.102016111321.2, filed on Jun. 21, 2016, which application is herebyincorporated herein by reference in its entirety.

TECHNICAL FIELD

Embodiments relate to backside contact concepts for semiconductordevices and in particular to methods for forming semiconductor devicesand semiconductor devices.

BACKGROUND

Vertical power technologies for Power MOSFETs(metal-oxide-semiconductor-field-effect-transistor) need a good adhesionat backside. No optimized adhesion in mass production may mean reducedyield due to metal lift off or even electrical overstress in field.There may be a demand to provide an improved concept for semiconductordevices, which may allow an increased manufacturing yield and/or areduced number of faulty devices.

SUMMARY

Some embodiments relate to a method for forming a semiconductor device.The method comprises forming a plurality of non-semiconductor materialportions at a first side of a semiconductor substrate and formingsemiconductor material on the plurality of non-semiconductor materialportions to bury the plurality of non-semiconductor material portionswithin semiconductor material. Further, the method comprises removing atleast a portion of the semiconductor substrate from a second side of thesemiconductor substrate to uncover the plurality of non-semiconductormaterial portions at a backside of the semiconductor device.Additionally, the method comprises forming a rough surface at thebackside of the semiconductor device by removing at least a subset ofthe plurality of non-semiconductor material portions while at least apart of a semiconductor material located laterally between the pluralityof non-semiconductor material portions remains or by removing at least apart of a semiconductor material located laterally between the pluralityof non-semiconductor material portions while the plurality ofnon-semiconductor material portions remain. Furthermore, the methodcomprises forming a backside metallization structure at the roughsurface.

Some embodiments relate to a semiconductor device comprising at leastone electrical element structure located at a front side of asemiconductor substrate. The at least one electrical element structureis configured to conduct current between the front side of thesemiconductor substrate and a back side of the semiconductor substratein a conductive state of the electrical element structure. Further, thesemiconductor device comprises a plurality of non-semiconductor materialportions located at a back side surface of the semiconductor substrate.A vertical distance of portions of the backside surface locatedlaterally between the plurality of non-semiconductor material portionsand surface portions of the plurality of non-semiconductor materialportions having the largest vertical distance to the back side surfaceof the semiconductor substrate is larger than 200 nm. Further, theplurality of non-semiconductor material portions comprises an electricalresistance lower than an electrical resistance of portions of thesemiconductor substrate. Additionally, the semiconductor devicecomprises a back side metallization structure arranged in contact withthe plurality of non-semiconductor material portions and portions of theback side surface of the semiconductor substrate located laterallybetween the plurality of non-semiconductor material portions.

Some embodiments relate to a semiconductor device comprising at leastone electrical element structure located at a front side of asemiconductor substrate. At least a rough portion of a backside surfaceof the semiconductor substrate comprises along at least one lateraldirection repeatedly plateaus and trenches. Further, the trenchescomprise substantially vertical side walls and a depth of the trenchesis larger than 200 nm. Additionally, the semiconductor device comprisesa back side metallization structure arranged in contact with at leastthe rough portion of the backside surface of the semiconductor substrateand a lead frame or printed circuit board electrically connected to theback side metallization structure.

BRIEF DESCRIPTION OF THE DRAWINGS

Some embodiments of apparatuses and/or methods will be described in thefollowing by way of example only, and with reference to the accompanyingfigures, in which:

FIG. 1 shows a flow chart of a method for forming a semiconductordevice;

FIGS. 2, 3 a, 3 b, 4 a, 4 b and 4 c show schematic cross sections ofportions of semiconductor devices at different manufacturing stages;

FIG. 5 shows a schematic cross section of a semiconductor device; and

FIG. 6 shows a schematic cross section of another semiconductor device.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Various example embodiments will now be described more fully withreference to the accompanying drawings in which some example embodimentsare illustrated. In the figures, the thicknesses of lines, layers and/orregions may be exaggerated for clarity.

Accordingly, while example embodiments are capable of variousmodifications and alternative forms, embodiments thereof are shown byway of example in the figures and will herein be described in detail. Itshould be understood, however, that there is no intent to limit exampleembodiments to the particular forms disclosed, but on the contrary,example embodiments are to cover all modifications, equivalents, andalternatives falling within the scope of the disclosure. Like numbersrefer to like or similar elements throughout the description of thefigures.

It will be understood that when an element is referred to as being“connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present. Other words used to describe therelationship between elements should be interpreted in a like fashion(e.g., “between” versus “directly between,” “adjacent” versus “directlyadjacent,” etc.).

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of exampleembodiments. As used herein, the singular forms “a,” “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises,” “comprising,” “includes” and/or “including,” when usedherein, specify the presence of stated features, integers, steps,operations, elements and/or components, but do not preclude the presenceor addition of one or more other features, integers, steps, operations,elements, components and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which example embodiments belong. Itwill be further understood that terms, e.g., those defined in commonlyused dictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art.However, should the present disclosure give a specific meaning to a termdeviating from a meaning commonly understood by one of ordinary skill,this meaning is to be taken into account in the specific context thisdefinition is given herein.

FIG. 1 shows a flow chart of a method for forming a semiconductor deviceaccording to an embodiment. The method 100 comprises forming no aplurality of non-semiconductor material portions at a first side of asemiconductor substrate and forming 120 semiconductor material on theplurality of non-semiconductor material portions to bury the pluralityof non-semiconductor material portions within semiconductor material.Further, the method 100 comprises removing 130 at least a portion of thesemiconductor substrate starting from a second side of the semiconductorsubstrate to uncover the plurality of non-semiconductor materialportions at a backside of the semiconductor device. Additionally, themethod 100 comprises forming 140 a rough surface at the backside of thesemiconductor device by removing at least a subset of the plurality ofnon-semiconductor material portions while at least a part of asemiconductor material located laterally between the plurality ofnon-semiconductor material portions remains or by removing at least apart of a semiconductor material located laterally between the pluralityof non-semiconductor material portions while the plurality ofnon-semiconductor material portions remain. Furthermore, the method 100comprises forming 150 a backside metallization structure at the roughsurface.

By burying non-semiconductor material structures within thesemiconductor material and removing the non-semiconductor material orsemiconductor material located between the non-semiconductor material, arough backside surface may be formable, which may be reproducible veryaccurately. In this way, the adhesion of the backside metallization atthe backside of the semiconductor device may be improved and/oradjustable very accurately and/or selectable in a wide range. Therefore,the manufacturing yield may be increased and/or a number of faultydevices may be reduced.

The plurality of non-semiconductor material portions may be formed nodirectly on the first side surface of the semiconductor substrate orwithin trenches extending into the semiconductor substrate. For example,a non-semiconductor material layer may be formed (e.g. deposited orgrown) on the semiconductor substrate and the non-semiconductor materiallayer may be structured (e.g. using a mask layer) to obtain theplurality of non-semiconductor material portions. Alternatively, one ormore (plurality) of trenches may be formed (e.g. etched) into thesemiconductor substrate from the first side of the semiconductorsubstrate and non-semiconductor material may be formed (e.g. depositedor grown) within the one or more trenches to obtain the plurality ofnon-semiconductor material portions. The non-semiconductor materialportions of the plurality of non-semiconductor material portions arearranged in a repetitive pattern. The plurality of non-semiconductormaterial portions may be separated from each other and may comprise eacha square shape, a rectangular shape, a circular shape, a ring shape(e.g. concentric rings) or a combination of these shapes in a top viewof the semiconductor device or may be arranged adjacent to each other toform a meander in a top view of the semiconductor device.

For example, each non-semiconductor material portion of the plurality ofnon-semiconductor material portions may comprise a vertical dimension orextension of more than 200 nm (or more than 500 nm, more than 1 μm ormore than 2 μm). Further, each non-semiconductor material portion of theplurality of non-semiconductor material portions may comprise a verticaldimension or extension of less than 5 μm (or less than 3 μm or less than2 μm). For example, each non-semiconductor material portion of theplurality of non-semiconductor material portions may comprise a lateralwidth of more than 100 nm (or more than 200 nm, more than 500 nm or morethan 1 μm). Further, each non-semiconductor material portion of theplurality of non-semiconductor material portions may comprise a lateralwidth of less than 3 μm (or less than 2 μm, or less than 1 μm). Keepingthe lateral width low may enable a large increase of the surface area atthe backside and/or may enable a low defect density for thesemiconductor material formed to cover the non-semiconductor materialportions due to an easier lateral overgrowth, for example. The lateralwidth of a non-semiconductor material portion may be a minimal lateraldimension of a non-semiconductor material portion or an average lateralwidth (e.g. averaged along a length of the non-semiconductor materialportion) of the non-semiconductor material portion.

For example, a (minimal) lateral distance between (each two) neighboringnon-semiconductor material portions of the plurality ofnon-semiconductor material portions along at least one (first) lateraldirection may be larger than 100 nm (or more than 200 nm, more than 500nm or more than 1 μm). The distance between non-semiconductor materialportions may be kept large enough to enable an epitaxial growth ofsemiconductor material between the non-semiconductor material portions,for example. Further, neighboring non-semiconductor material portions ofthe plurality of non-semiconductor material portions along a secondlateral direction orthogonal to the first lateral direction may bearranged adjacent to each other or may be spaced apart from each otherby more than 200 nm as well. Further, a (minimal) lateral distancebetween (each two) neighboring non-semiconductor material portions ofthe plurality of non-semiconductor material portions along at least onelateral direction may be less than 20 μm (or less than 10 μm, less than5 μm, less than 3 μm or less than 1 μm). Keeping the distance betweenneighboring non-semiconductor material portions low may enable a largeincrease of the surface area at the backside, for example.

For example, the plurality of non-semiconductor material portionscomprise or consist of insulating material (e.g. silicon oxide orsilicon nitride), carbide, ternary carbide, ternary nitride and/ormetal.

Semiconductor material may be formed 120 (e.g. deposited or grown)directly on the non-semiconductor material portions and directly onportions of the semiconductor substrate located laterally between thenon-semiconductor material portions. For example, the semiconductormaterial may be epitaxially grown so that the crystal lattice of thesemiconductor substrate is reproduced and continued by the grownsemiconductor material. For example, the semiconductor material formed120 on the non-semiconductor material portions has the same materialcomposition as the semiconductor substrate. For example, thenon-semiconductor material portions may be covered due to a lateralovergrowth during the epitaxially growth of the semiconductor material.In other words, the formation 120 of the semiconductor material on theplurality of non-semiconductor material portions may compriseepitaxially growing the semiconductor material so that the plurality ofnon-semiconductor material portions are buried within semiconductormaterial (of the semiconductor substrate and semiconductor materialformed on the non-semiconductor material portions) due to lateralovergrowth.

For example, the semiconductor material may be formed on the pluralityof non-semiconductor material portions with an arbitrary thicknesslarger than two times a minimal lateral width of the non-semiconductormaterial portions (e.g. to enable a lateral overgrowth). For example,the thickness of the semiconductor material above the non-semiconductormaterial portions may be selected depending on the type and/or voltageclass of electrical element structures of the semiconductor device (e.g.to be formed at the surface of the semiconductor material). For example,the thickness (e.g. measured vertically between the non-semiconductormaterial portions and a surface of the semiconductor material) of thesemiconductor material formed on the plurality of non-semiconductormaterial portions may be larger than 2 μm (or larger than 5 μm, largerthan 10 μm, larger than 20 μm, larger than 50 μm or larger than 100 μm).

At least a portion of the semiconductor substrate may be removed 130 bygrinding, etching (wet or dry chemical etching) and/or chemicalmechanical polishing CMP until the non-semiconductor material portionsof the plurality of non-semiconductor material portions are exposed atthe backside of the semiconductor device. For example, the wholesemiconductor substrate may be removed, if the non-semiconductormaterial portions were deposited and structured on the first surface ofthe semiconductor substrate. Alternatively, portions of thesemiconductor substrate may remain laterally between thenon-semiconductor material portions after the removal 130, if thenon-semiconductor material portions were formed in trenches extendinginto the semiconductor substrate.

After uncovering the non-semiconductor material portions by removing 130the semiconductor substrate, a substantially planar surface may beobtained at the backside of the semiconductor substrate. The planarsurface may comprise surface portions formed by the non-semiconductormaterial portions and surface portions formed by semiconductor material(of the semiconductor substrate or the semiconductor material formedbetween the non-semiconductor material portions). Starting from thesubstantially planar backside surface, a rough surface may be obtainedby removing the non-semiconductor material portions or removing at leastportions of the semiconductor material located laterally between thenon-semiconductor material portions.

For example, the rough surface may be formed 140 by removing at least apart of a semiconductor material located laterally between the pluralityof non-semiconductor material portions while the plurality ofnon-semiconductor material portions remain (e.g. FIGS. 3b and 4c ). Forexample, the non-semiconductor material portions may compriseelectrically conductive material (e.g. ternary carbide, ternary nitrideor metal) so that an on-resistance of a vertical electrical element(e.g. diode or transistor conducting current between front side andbackside) of the semiconductor device may be kept low or may beimproved.

Alternatively, the rough surface may be formed 140 by removing at leasta subset of the plurality of non-semiconductor material portions whileat least a part of the semiconductor material located laterally betweenthe plurality of non-semiconductor material portions remains (e.g. FIGS.4a and 4b ). For example, all non-semiconductor material portions may beremoved or a subset of the non-semiconductor material portions (e.g.comprising insulating material) located in a predefined area (e.g. edgetermination region) may remain at the backside. For example, a masklayer (e.g. photo resist or hard mask) may be formed at an edgetermination region at the backside of the semiconductor device andnon-semiconductor material portions of the plurality ofnon-semiconductor material portions are removed at regions uncovered bythe mask layer (and others remain at the edge termination region coveredby the mask layer). In this way, the emitter efficiency in one or morepredefined areas may be adjusted (e.g. reduced) to a desired level, forexample.

A rough surface may be a surface comprising a roughness (e.g. differencebetween maximal peak height and maximal valley depth) of more than 200nm (or more than 500 nm, more than 1 μm or more than 2 μm).

The backside metallization structure comprises at least a metal layerand optionally a barrier layer and may be formed 150 by depositing atleast a metal layer (e.g. aluminum or copper) or a barrier layer (e.g.titanium and/or titanium nitride) and a metal layer (directly) on therough surface represented by surface portions of the non-semiconductormaterial portions and surface portions of semiconductor material locatedlaterally between the non-semiconductor material portions, if thenon-semiconductor material portions remain, or the backside surface ofthe semiconductor material, if the non-semiconductor material portionsare removed. For example, the backside metallization structure is incontact with the plurality of non-semiconductor material portions, ifthe non-semiconductor material portions remain.

For example, the method 100 further comprises forming electrical elementstructures (e.g. transistors) at a front side of the semiconductordevice (e.g. at a surface of the semiconductor material formed on thenon-semiconductor material portions). The electrical element structuresmay be a transistor cell of a transistor arrangement (comprising aplurality of transistor cells connected in parallel) or the electricalelement structure may comprise one or more transistor cells, forexample.

The semiconductor substrate of the semiconductor device may be a siliconsubstrate. Alternatively, the semiconductor substrate may be a wide bandgap semiconductor substrate having a band gap larger than the band gapof silicon (1.1 eV). For example, the semiconductor substrate may be asilicon carbide (SiC)-based semiconductor substrate, a silicon germanium(SiGe) based semiconductor substrate, or gallium arsenide (GaAs)-basedsemiconductor substrate, or a gallium nitride (GaN)-based semiconductorsubstrate. The semiconductor substrate may be a semiconductor wafer.

For example, doping regions for electrical element structures may beformed at a (front side) surface of the semiconductor material formed onthe non-semiconductor material portions and a wiring layer stack (e.g.including wiring structures and contact pads implemented by one or moremetal layers and one or more via layers) may be formed on the (frontside) surface of the semiconductor material before removing 130 at leastthe portion of the semiconductor substrate from the backside.Additionally, dopants may be implanted into a backside surface regionbefore forming the backside metallization structure to increase a dopingconcentration in a portion of the semiconductor material located at thebackside surface to enable an ohmic contact, for example. For example, aplurality of semiconductor devices may be formed on a semiconductorwafer and may be separated from each other after forming 150 thebackside metallization structure. For example, the semiconductor devicemay be attached or assembled to a lead frame or a printed circuit boardPCB (e.g. chip embedding) by soldering the backside metallizationstructure to a lead frame or a printed circuit board.

For example, a vertical direction, a vertical dimension or verticalextension and a thickness of a structure or a layer may be measuredorthogonal to a first side surface (e.g. front side surface or mainsurface) of the semiconductor substrate and a lateral direction and alateral dimension or lateral extension may be measured in parallel tothe first side surface of the semiconductor substrate.

The front side of the semiconductor device may be the surface used toimplement more sophisticated and complex structures than at the backside, since the process parameters (e.g. temperature) and the handlingmay be limited for the back side, if structures are already formed atone side of the semiconductor substrate, for example.

For example, the semiconductor device may be an integrated circuit, aprocessor device, a memory device, a sensor device or a powersemiconductor device. For example, the semiconductor device comprisesone or more electrical element structures (e.g. a diode structure or atransistor structure, for example an Insulated-Gate Bipolar Transistor(IGBT) or a Field Effect Transistor (FET)). For example, the (power)semiconductor device may comprise one or more vertical electricalelement structures conducting a current (e.g. vertical diode) orcontrolling a current (e.g. vertical transistor) between a front side ofthe semiconductor device and a backside of the semiconductor device. Dueto the vertical current flow, a reliable contact between the backside ofthe semiconductor substrate and a backside metallization may beimportant. A power semiconductor device or an electrical elementstructure (e.g. transistor structure or diode structure) of the powersemiconductor device may have a breakdown voltage or blocking voltage ofmore than boy (e.g. a breakdown voltage of 10 V, 20 V or 50V), more than100 V (e.g. a breakdown voltage of 200 V, 300 V, 400V or 500V) or morethan 500 V (e.g. a breakdown voltage of 600 V, 700 V, 800V or 1000V) ormore than 500 V (e.g. a breakdown voltage of 1200 V, 1500 V, 1700V,2000V, 3300V or 6500V), for example.

FIGS. 2, 3 a, 3 b, 4 a, 4 b and 4 c show schematic cross sections ofportions of semiconductor devices at different manufacturing stages of amethod for forming semiconductor devices according to an embodiment.FIG. 2 shows a portion of a semiconductor wafer 210 (e.g. siliconsubstrate) and a plurality of non-semiconductor material portions 220(buried structures) is formed (e.g. deposited and structured) at asurface of the semiconductor wafer 210. Further, semiconductor material230 (e.g. silicon) is formed (e.g. by epitaxial lateral overgrowth ELO)on the plurality of non-semiconductor material portions 220 (e.g. oxide,carbide, ternary carbides or ternary nitrides). Then the semiconductorwafer 210 is removed from the backside by CMP, mechanical grindingand/or etching. The removal of semiconductor material may be stopped assoon as the plurality of non-semiconductor material portions 220 areuncovered as shown in FIG. 3a or (additionally or directly) an etchingmay be continued or performed to remove additionally some of thesemiconductor material located laterally between the plurality ofnon-semiconductor material portions 220 as shown in FIG. 3 b.

Afterwards, the plurality of non-semiconductor material portions 220 maybe removed as shown in FIGS. 4a and 4b . FIG. 4a shows an example forremoving the plurality of non-semiconductor material portions 220 afterobtaining a substantially planar surface after removing thesemiconductor wafer as shown in FIG. 3a . FIG. 4b shows an example forremoving the plurality of non-semiconductor material portions 220 afteretching back the semiconductor material between the plurality ofnon-semiconductor material portions 220 as shown in FIG. 3b . In thisexample, the buried structures may be eliminated (e.g. by etching).

Alternatively, the buried structures may remain after etching back thesemiconductor material (e.g. FIG. 3b ) between the plurality ofnon-semiconductor material portions 220 as shown in FIG. 4c . In thisexample, the plurality of non-semiconductor material portions 220 maycomprise electrically conductive material (e.g. ternary carbides orternary nitrides).

More details and aspects of the method for forming semiconductor devicesshown in FIG. 2-4 c are mentioned in connection with the proposedconcept or one or more examples described above. The method may compriseone or more additional optional features corresponding to one or moreaspects of the proposed concept or one or more examples described above(e.g. FIG. 1) or below (e.g. FIG. 5-6).

FIG. 5 shows a schematic cross section of a semiconductor deviceaccording to an embodiment. The semiconductor device 500 comprises atleast one electrical element structure 510 located at a front side of asemiconductor substrate 502. The at least one electrical elementstructure 510 is configured to conduct current between the front side ofthe semiconductor substrate 502 and a back side of the semiconductorsubstrate 502 in a conductive state of the electrical element structure510. Further, the semiconductor device 500 comprises a plurality ofnon-semiconductor material portions 520 located at a back side surfaceof the semiconductor substrate 502. A vertical distance of portions ofthe backside surface of the semiconductor substrate 502 locatedlaterally between the plurality of non-semiconductor material portions520 and surface portions of the plurality of non-semiconductor materialportions 520 having the largest vertical distance to the back sidesurface of the semiconductor substrate 502 is larger than 200 nm (ormore than 500 nm, more than 1 μm or more than 2 μm). Further, theplurality of non-semiconductor material portions 520 comprise anelectrical resistance lower than an electrical resistance of portions ofthe semiconductor substrate 502. Additionally, the semiconductor device500 comprises a back side metallization structure 530 arranged incontact with the plurality of non-semiconductor material portions 520and portions of the back side surface of the semiconductor substrate 502located laterally between the plurality of non-semiconductor materialportions 520.

By burying non-semiconductor material structures within thesemiconductor material, a rough backside surface may be formable, whichmay be reproducible very accurately. In this way, the adhesion of thebackside metallization at the backside of the semiconductor device maybe improved and/or adjustable very accurately and/or selectable in awide range. Therefore, the manufacturing yield may be increased and/or anumber of faulty devices may be reduced.

For example, the material of the plurality of non-semiconductor materialportions 520 comprise an electrical resistance lower than (e.g. lowerthan 50%, lower than 10% or lower than 1%) an electrical resistance of aportion of the semiconductor substrate 502 (e.g. a drift region, bodyregion and/or source region of the at least one electrical elementstructure).

For example, the electrical element structure 510 may be a verticaltransistor structure conducting current between the front side of thesemiconductor substrate 502 and the back side of the semiconductorsubstrate 502 in an on-state of the vertical transistor structure.Alternatively, the electrical element structure 510 may be a verticaldiode structure conducting current between the front side of thesemiconductor substrate 502 and the back side of the semiconductorsubstrate 502 in a forward biased state of the vertical diode structure.

The semiconductor substrate of the semiconductor device 500 maycorrespond to the semiconductor material formed on the non-semiconductormaterial portions (and optionally portions of the semiconductorsubstrate) mentioned in connection with FIG. 1, for example.

More details and aspects of the semiconductor device 500 are mentionedin connection with the proposed concept or one or more examplesdescribed above. The semiconductor device 500 may comprise one or moreadditional optional features corresponding to one or more aspects of theproposed concept or one or more examples described above (e.g. FIG. 1-4c) or below (e.g. FIG. 6).

FIG. 6 shows a schematic cross section of a semiconductor deviceaccording to an embodiment. The semiconductor device 600 comprising atleast one electrical element structure 510 located at a front side of asemiconductor substrate 502. At least a rough portion of a backsidesurface of the semiconductor substrate 502 comprises along at least onelateral direction repeatedly plateaus 621 and trenches 622. Further, thetrenches 622 may comprise substantially vertical side walls. Further, adepth of the trenches 622 is larger than 200 nm (or more than 500 nm,more than 1 μm or more than 2 μm). Additionally, the semiconductordevice 600 comprises a back side metallization structure 530 arranged incontact with at least the rough portion of the backside surface of thesemiconductor substrate 502 and a lead frame or printed circuit board640 electrically connected to the back side metallization structure 530.

By generating a rough backside surface with plateaus and trenches withsubstantially vertical side walls, the adhesion of the backsidemetallization at the backside of the semiconductor device may beimproved and/or adjustable very accurately and/or selectable in a widerange. Therefore, the manufacturing yield may be increased and/or anumber of faulty devices may be reduced.

For example, the rough portion of the backside surface of thesemiconductor substrate 502 may be located at an active area of thesemiconductor substrate (e.g. leaving out an edge termination region) ormay extend over the whole backside surface of the semiconductorsubstrate 502.

For example, the rough portion of the backside surface of thesemiconductor substrate 502 comprises along at least one lateraldirection repeatedly plateaus 621 and trenches 622, if the plateaus 621and/or trenches 622 are strip-shaped or meander-shaped, for example.Alternatively, the rough portion of the backside surface of thesemiconductor substrate 502 comprises along two orthogonal lateraldirections repeatedly plateaus 621 and trenches 622, if the plateaus 621or trenches 622 are square-shaped or rectangular-shaped, for example.

The back side metallization structure 530 may be in contact with atleast the (whole) rough portion of the backside surface of thesemiconductor substrate 502 or the whole backside surface of thesemiconductor substrate 502.

For example, the back side metallization structure 530 may be solderedto the lead frame or printed circuit board 640.

For example, a portion of the semiconductor substrate located closerthan 200 nm to the backside surface of the semiconductor substrate maycomprise a crystal defect density of more than 1000 per cm³ (or morethan 10000 per cm³ or more than 1000000 per cm³). A high defect densityclose to the backside surface of the semiconductor substrate may existdue to the manufacturing of the rough surface. For example,non-semiconductor material portions may be laterally overgrown bysemiconductor material as described in connection with FIG. 1, forexample. The semiconductor material formed close to thenon-semiconductor material portions may comprise an increased defectdensity, which may remain after removing the non-semiconductor materialportions. For example, an increased number of sidewall defects of theepi along the buried structures may be detectable (although thenon-semiconductor material portions may be removed afterwards).

An angle between the substantially vertical side walls of the trenchesand a front side surface of the semiconductor substrate may be between70° and 110° (or between 80° and 100° or between 85° and 95°).

The semiconductor substrate of the semiconductor device 500 maycorrespond to the semiconductor material formed on non-semiconductormaterial portions (and optionally portions of the semiconductorsubstrate) mentioned in connection with FIG. 1, for example.

More details and aspects of the semiconductor device 600 are mentionedin connection with the proposed concept or one or more examplesdescribed above. The semiconductor device 600 may comprise one or moreadditional optional features corresponding to one or more aspects of theproposed concept or one or more examples described above (e.g. FIG. 1-5)or below.

Some embodiments relate to power devices with roughen backside BS foroptimized adhesion. Defined roughening of power devices e.g. MOSFETsbackside for reproducible adhesion of the backside metallization may beenabled. Furthermore, backside gettering techniques may be improved andalso the removal of vacancy cluster-induced defects by a well-definedoxidation of the wafer backside may be enabled. Additionally, voids,which have been caused by the solder process, may be reduced or avoided.

Another concept to optimize adhesion may be to increase roughening ofSilicon backside by wet etching, mechanical grinding or a combination ofboth. However, by using e.g. a grinding method there may be a Gaussdistribution of roughening and as consequence also of the adhesion overa wafer lot. Additionally the total thickness variation may be dependentfrom etching and grinding time, but also from consistency of wet etchand abrasion of the grinding material.

A reproducible roughening may be structured by using an integrated etchstop e.g. based on buried oxide or buried carbide structures withbackside etch stop in combination with different etching and thinningmethods. Alternatively the buried structures may be realized also withternary carbides or ternary nitrides, for example.

The backside thinning process itself may be implemented by or incombination with wet etch, dry etch, mechanical grinding and chemicalmechanical polishing (CMP). In case of e.g. CMP, grinding or anisotropicetching the thinning process may stop at the buried structures e.g. bydetection signal (e.g. FIG. 3a ). In case of directly or additionallyetching e.g. isotropic or crystal etching (e.g. having crystal directiondepending different etch rates) the process may stop between sidewallsof structures (e.g. FIG. 3b ). In case A (e.g. FIG. 4a ) the buriedstructures as oxide or carbide may be finally eliminated e.g. byetching. As a result of this the final height and sidewall of remainingSi may be defining the roughening of backside; e.g. the roughness may bedefined in a well-controlled manner by the design of the buriedstructures and the depth of the etching grooves between. In case B (e.g.FIG. 4c ) the buried structures remain as ternary nitrides or ternarycarbides, for example. Here FIG. 3b may be already describing the finalroughening of the backside. Based on that, a realization of a meander(e.g. shape of the rough surface in a cross section) similar rougheningmay be possible and also reproducible in mass production.

The proposed concept may deal with a reproducible roughening for anoptimized or improved adhesion.

Optionally, it may be possible that at least some of the oxide areas(non-semiconductor material portions) may remain on the backside toprovide a well-defined local isolation of the wafer. An application maybe a local reduction of the emitter efficiency in the area of thejunction termination. Furthermore, it may be possible to provide a localroughening of the wafer backside which might not be feasible bymechanical treatments, for example.

Example embodiments may further provide a computer program having aprogram code for performing one of the above methods, when the computerprogram is executed on a computer or processor. A person of skill in theart would readily recognize that acts of various above-described methodsmay be performed by programmed computers. Herein, some exampleembodiments are also intended to cover program storage devices, e.g.,digital data storage media, which are machine or computer readable andencode machine-executable or computer-executable programs ofinstructions, wherein the instructions perform some or all of the actsof the above-described methods. The program storage devices may be,e.g., digital memories, magnetic storage media such as magnetic disksand magnetic tapes, hard drives, or optically readable digital datastorage media. Further example embodiments are also intended to covercomputers programmed to perform the acts of the above-described methodsor (field) programmable logic arrays ((F)PLAs) or (field) programmablegate arrays ((F)PGAs), programmed to perform the acts of theabove-described methods.

The description and drawings merely illustrate the principles of thedisclosure. It will thus be appreciated that those skilled in the artwill be able to devise various arrangements that, although notexplicitly described or shown herein, embody the principles of thedisclosure and are included within its spirit and scope. Furthermore,all examples recited herein are principally intended expressly to beonly for pedagogical purposes to aid the reader in understanding theprinciples of the disclosure and the concepts contributed by theinventor(s) to furthering the art, and are to be construed as beingwithout limitation to such specifically recited examples and conditions.Moreover, all statements herein reciting principles, aspects, andembodiments of the disclosure, as well as specific examples thereof, areintended to encompass equivalents thereof.

It should be appreciated by those skilled in the art that any blockdiagrams herein represent conceptual views of illustrative circuitryembodying the principles of the disclosure. Similarly, it will beappreciated that any flow charts, flow diagrams, state transitiondiagrams, pseudo code, and the like represent various processes whichmay be substantially represented in computer readable medium and soexecuted by a computer or processor, whether or not such computer orprocessor is explicitly shown.

Furthermore, the following claims are hereby incorporated into theDetailed Description, where each claim may stand on its own as aseparate embodiment. While each claim may stand on its own as a separateembodiment, it is to be noted that—although a dependent claim may referin the claims to a specific combination with one or more otherclaims—other embodiments may also include a combination of the dependentclaim with the subject matter of each other dependent or independentclaim. Such combinations are proposed herein unless it is stated that aspecific combination is not intended. Furthermore, it is intended toinclude also features of a claim to any other independent claim even ifthis claim is not directly made dependent to the independent claim.

It is further to be noted that methods disclosed in the specification orin the claims may be implemented by a device having means for performingeach of the respective acts of these methods.

Further, it is to be understood that the disclosure of multiple acts orfunctions disclosed in the specification or claims may not be construedas to be within the specific order. Therefore, the disclosure ofmultiple acts or functions will not limit these to a particular orderunless such acts or functions are not interchangeable for technicalreasons. Furthermore, in some embodiments a single act may include ormay be broken into multiple sub acts. Such sub acts may be included andpart of the disclosure of this single act unless explicitly excluded.

What is claimed is:
 1. A method for forming a semiconductor device, themethod comprising: forming a plurality of non-semiconductor materialportions at a first side of a semiconductor substrate; formingsemiconductor material on the plurality of non-semiconductor materialportions to bury the plurality of non-semiconductor material portionswithin semiconductor material; removing at least a portion of thesemiconductor substrate from a second side of the semiconductorsubstrate to uncover the plurality of non-semiconductor materialportions at a backside of the semiconductor device; forming a roughsurface at the backside of the semiconductor device by removing at leasta subset of the plurality of non-semiconductor material portions whileat least a part of a semiconductor material located laterally betweenthe plurality of non-semiconductor material portions remains or byremoving at least a part of a semiconductor material located laterallybetween the plurality of non-semiconductor material portions while theplurality of non-semiconductor material portions remain; and forming abackside metallization structure at the rough surface.
 2. The methodaccording to claim 1, wherein the plurality of non-semiconductormaterial portions comprise a vertical dimension of more than 200 nm. 3.The method according to claim 1, wherein the plurality ofnon-semiconductor material portions comprise a vertical dimension ofless than 5 μm.
 4. The method according to claim 1, wherein theplurality of non-semiconductor material portions comprise a lateralwidth of more than 100 nm.
 5. The method according to claim 1, whereinthe plurality of non-semiconductor material portions comprise a lateralwidth of less than 3 μm.
 6. The method according to claim 1, wherein alateral distance between neighboring non-semiconductor material portionsof the plurality of non-semiconductor material portions along at leastone lateral direction is larger than 100 nm.
 7. The method according toclaim 1, wherein a lateral distance between neighboringnon-semiconductor material portions of the plurality ofnon-semiconductor material portions along at least one lateral directionis less than 20 μm.
 8. The method according to claim 1, wherein formingthe plurality of non-semiconductor material portions comprises forming aplurality of trenches and forming non-semiconductor material within theplurality of trenches or forming a non-semiconductor material layer onthe semiconductor substrate and structuring the non-semiconductormaterial layer.
 9. The method according to claim 1, wherein a thicknessof the semiconductor material formed on the plurality ofnon-semiconductor material portions is larger than 2 μm.
 10. The methodaccording to claim 1, wherein forming semiconductor material on theplurality of non-semiconductor material portions comprises epitaxiallygrowing the semiconductor material so that the plurality ofnon-semiconductor material portions are buried due to lateralovergrowth.
 11. The method according to claim 1, wherein thenon-semiconductor material portions of the plurality ofnon-semiconductor material portions are arranged in a repetitivepattern.
 12. The method according to claim 1, wherein the plurality ofnon-semiconductor material portions comprise insulating material. 13.The method according to claim 1, further comprising forming a mask layerat an edge termination region at the backside of the semiconductorsubstrate before removing non-semiconductor material portions, whereinnon-semiconductor material portions of the plurality ofnon-semiconductor material portions are removed at regions uncovered bythe mask layer.
 14. The method according to claim 1, wherein theplurality of non-semiconductor material portions comprise ternarycarbide, ternary nitride or metal.
 15. The method according to claim 1,wherein the backside metallization structure is in contact with theplurality of non-semiconductor material portions.
 16. The methodaccording to claim 1, further comprising forming a plurality ofelectrical element structures at a surface of the semiconductor materialformed on the plurality of non-semiconductor material portions.
 17. Themethod according to claim 1, further comprising soldering the backsidemetallization structure to a lead frame or a printed circuit board. 18.A semiconductor device comprising: at least one electrical elementstructure located at a front side of a semiconductor substrate, whereinthe at least one electrical element structure is configured to conductcurrent between the front side of the semiconductor substrate and abackside of the semiconductor substrate in a conductive state of theelectrical element structure; a plurality of non-semiconductor materialportions located at a backside surface of the semiconductor substrate,wherein a vertical distance of portions of the backside surface locatedlaterally between the plurality of non-semiconductor material portionsand surface portions of the plurality of non-semiconductor materialportions having a largest vertical distance to the backside surface ofthe semiconductor substrate is larger than 200 nm, wherein the pluralityof non-semiconductor material portions comprises an electricalresistance lower than an electrical resistance of portions of thesemiconductor substrate; and a backside metallization structure arrangedin contact with the plurality of non-semiconductor material portions andportions of the backside surface of the semiconductor substrate locatedlaterally between the plurality of non-semiconductor material portions.19. A semiconductor device comprising: at least one electrical elementstructure located at a front side of a semiconductor substrate, whereinat least a rough portion of a backside surface of the semiconductorsubstrate comprises along at least one lateral direction repeatedlyplateaus and trenches, wherein the trenches comprise substantiallyvertical side walls and a depth of the trenches is larger than 200 nm; abackside metallization structure arranged in contact with at least therough portion of the backside surface of the semiconductor substrate;and a lead frame or printed circuit board electrically connected to thebackside metallization structure.
 20. The semiconductor device accordingto claim 19, wherein a portion of the semiconductor substrate locatedcloser than 200 nm to the backside surface of the semiconductorsubstrate comprises a crystal defect density of more than 1000 per cm³.